Heat pump system and control method thereof

ABSTRACT

The present disclosure provides a heat pump system and a control method. The heat pump system includes a compressor, a first flow path, a second flow path and a third flow path. The second end of the first flow path, the second end of the second flow path and the second end of the third flow path are connected. Two of the first end of the first flow path, the first end of the second flow path and the first end of the third flow path are connected to the inlet and outlet of the compressor in specific modes through a switching assembly so that the heat pump system can operate in one or more of a cooling mode, a heating mode, a hot water preparing mode and a cooling heat recovery mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Chinese Application No. 202010758274.2 filed Jul. 31, 2020, the disclosure of which is incorporated herein by reference in its entirety

BACKGROUND

The present disclosure relates to the technical field of air conditioning and domestic hot water supply device. More specifically, the present disclosure relates to a heat pump system and a control method thereof.

At present, modular heat pump systems often have multiple paths to meet air conditioning requirements and optional domestic hot water requirements. The various modes are realized through adjustments implemented by a four-way valve and throttling devices on the flow paths. A common setting is that each flow path is equipped with a throttling device and a check valve connected in parallel with it, and each throttling device functions in a different mode.

BRIEF DESCRIPTION

An object of the present disclosure is to solve or at least alleviate the problems existing in the prior art.

In one aspect, a heat pump system is provided, which includes:

a compressor;

a first flow path, which includes a first end of the first flow path, a first heat exchanger, a first throttling device, and a second end of the first flow path in sequence;

a second flow path, which includes a first end of a second flow path, a second heat exchanger, a second throttling device, and a second end of the second flow path in sequence;

a third flow path, which includes a first end of the third flow path, a third heat exchanger, a first check valve, and a second end of the third flow path in sequence, wherein the first check valve on the third flow path only allows a fluid flowing in a direction toward the second end of the third flow path to pass through;

wherein the second end of the first flow path, the second end of the second flow path and the second end of the third flow path are connected; and

a switching assembly, which can be switched between any two, three or four of the following connection modes:

a first connection mode, in which the first end of the first flow path is connected to an outlet of the compressor, and the first end of the second flow path is connected to an inlet of the compressor;

a second connection mode, in which the first end of the second flow path is connected to the outlet of the compressor, and the first end of the first flow path is connected to the inlet of the compressor;

a third connection mode, in which the first end of the third flow path is connected to the outlet of the compressor, and the first end of the first flow path is connected to the inlet of the compressor; and

a fourth connection mode, in which the first end of the third flow path is connected to the outlet of the compressor, and the first end of the second flow path is connected to the inlet of the compressor; and

a control system, which enables the heat pump system to operate in any two, three, or four of a cooling mode, a heating mode, a hot water preparing mode, and a cooling heat recovery mode;

in the cooling mode, the switching assembly is switched to the first connection mode, the first throttling device plays a throttling function, and the second throttling device is fully opened or bypassed;

in the heating mode, the switching assembly is switched to the second connection mode, the first throttling device plays a throttling function, and the second throttling device is bypassed;

in the hot water preparing mode, the switching assembly is switched to the third connection mode, the first throttling device plays a throttling function, and the second throttling device is in a closed state; and

in the cooling heat recovery mode, the switching assembly is switched to the fourth connection mode, the second throttling device plays a throttling function, and the first throttling device is in a closed state.

Optionally, in the heat pump system, the second flow path includes a second check valve connected in parallel with the second throttling device, and the second check valve only allows a fluid flowing in a direction toward the second end of the second flow path to pass through.

Optionally, in the heat pump system, the second flow path includes a solenoid valve connected in parallel with the second throttling device, and in the cooling mode, the heat pump system opens the solenoid valve and closes the second throttling device to bypass the second throttling device.

Optionally, in the heat pump system, the heat pump system further includes a receiver, and the receiver includes a single pipeline and is connected to or near a position where the second end of the first flow path, the second end of the second flow path and the second end of the third flow path are connected.

Optionally, in the heat pump system, the heat pump system further includes a receiver which includes a first pipeline and a second pipeline, the second end of the first flow path and the second end of the second flow path are connected to the first pipeline of the receiver, and the second end of the third flow path is connected to the second pipeline of the receiver.

Optionally, in the heat pump system, the heat pump system further includes a solenoid valve, which is connected between the second pipeline of the receiver and a position between the second heat exchanger and the second throttling device on the second flow path.

Optionally, in the heat pump system, the heat pump system further includes a second check valve, which is connected between the second pipeline of the receiver and a position between the second heat exchanger and the second throttling device on the second flow path, and which only allows a fluid flowing in a direction toward a second end of the second pipeline to pass through.

Optionally, in the heat pump system, the heat pump system includes a cooling working condition, and under the cooling working condition, the heat pump system is switched among the cooling mode, the hot water preparing mode, and the cooling heat recovery mode.

Optionally, in the heat pump system, the heat pump system includes a heating working condition, and under the heating working condition, the heat pump system is switched between the heating mode and the hot water preparing mode, wherein the heat pump system performs defrosting by being switched to the first connection mode and fully opening the first throttling device.

Optionally, in the heat pump system, the compressor is an enhanced vapor injection compressor, the heat pump system further includes an economizer, and the first flow path includes a branch point and passes through a first pipeline of the economizer, wherein in the heating mode and the hot water preparing mode, a refrigerant flowing from the second end of the first flow path toward the first end of the first flow path passes through the first pipeline of the economizer before passing through the first throttling device, and is divided at the branch point into a first part leading to the first throttling device and a second part leading to a branch; the second part of the refrigerant passes through a branch throttling device on the branch and a second pipeline of the economizer to exchange heat with the refrigerant in the first pipeline of the economizer, and the refrigerant passing through the second pipeline of the economizer is supplied to an enhanced vapor injection port of the compressor.

Optionally, in the heat pump system, the third flow path does not have a throttling device.

Optionally, in the heat pump system, the switching assembly includes two four-way valves.

In another aspect, a control method of a heat pump system is provided, which includes: operating the heat pump system in any two, three, or four of a cooling mode, a heating mode, a hot water preparing mode, and a cooling heat recovery mode; wherein:

in the cooling mode, the first end of the first flow path is connected to the outlet of the compressor, the first end of the second flow path is connected to the inlet of the compressor, the first throttling device plays a throttling function, and the second throttling device is fully opened or bypassed;

in the heating mode, the first end of the second flow path is connected to the outlet of the compressor, the first end of the first flow path is connected to the inlet of the compressor, the first throttling device plays a throttling function, and the second throttling device is bypassed;

in the hot water preparing mode, the first end of the third flow path is connected to the outlet of the compressor, the first end of the first flow path is connected to the inlet of the compressor, the first throttling device plays a throttling function, and the second throttling device is in a closed state; and

in the cooling heat recovery mode, the first end of the third flow path is connected to the outlet of the compressor, the first end of the first flow path is connected to the inlet of the compressor, the second throttling device plays a throttling function, and the first throttling device is in a closed state.

Optionally, the method includes operating the heat pump system under a cooling working condition, wherein the heat pump system is switched among the cooling mode, the hot water preparing mode, and the cooling heat recovery mode.

Optionally, the method includes operating the heat pump system under a heating working condition, wherein the heat pump system is switched between the heating mode and the hot water preparing mode; optionally, under the heating working condition, the first end of the first flow path is connected to the outlet of the compressor, the first end of the second flow path is connected to the inlet of the compressor, and the first throttling device is fully opened to perform defrost.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the accompanying drawings, the disclosure of the present invention will become easier to understand. It can be easily understood by those skilled in the art that these drawings are only for illustrative purpose, and are not intended to limit the scope of protection of the present invention. In addition, similar numbers in the drawings are used to denote similar components, in which:

FIGS. 1 to 4 show schematic structural diagrams of a heat pump system in different working modes according to an embodiment;

FIG. 5 shows a schematic structural diagram of a heat pump system according to another embodiment;

FIGS. 6 to 9 show schematic structural diagrams of a heat pump system in different working modes according to another embodiment; and

FIG. 10 shows a schematic structural diagram of a heat pump system according to another embodiment.

DETAILED DESCRIPTION

First, referring to FIG. 1, a heat pump system according to an embodiment of the present disclosure will be introduced. The heat pump system may include: a compressor 4, a switching assembly 90, a first flow path 100, a second flow path 200, a third flow path 300, and a control system (not shown). The compressor 4 may include an inlet 42 of the compressor and an outlet 41 of the compressor. In some embodiments, a separator 6 may be provided upstream of the inlet 42 of the compressor to remove liquid in the return fluid. The first flow path 100 may include a first end 11 of the first flow path, a first heat exchanger 12, a first throttling device 13 and a second end 14 of the first flow path in sequence. In some embodiments, the first heat exchanger 12 may be a coil heat exchanger and may be located outdoor. The second flow path 200 may include a first end 21 of the second flow path, a second heat exchanger 22, a second throttling device 23, and a second end 24 of the second flow path in sequence. In some embodiments, the second heat exchanger 22 may be a brazed plate heat exchanger and may be located indoor. The third flow path 300 may include a first end 31 of the third flow path, a third heat exchanger 32, a first check valve 33 and a second end 34 of the third flow path. In the following, for the sake of clarity, a direction from the first end to the second end of each flow path is defined as a first flow direction of each flow path, and a direction from the second end to the first end of each flow path is defined as a second flow direction of each flow path. The first check valve 33 on the third flow path only allows a fluid flowing in a direction toward the second end of the third flow path, that is, it only allows the fluid flowing in the first flow direction in the third flow path to pass through. In some embodiments, the first flow path 100 may include a filter 15 between the first heat exchanger 12 and the first throttling device 13. In some embodiments, the second flow path 200 may include a filter 25 between the second heat exchanger 22 and the second throttling device 23. In some embodiments, the third flow path 300 may include a filter 35 between the third heat exchanger 32 and the first check valve 33. In the embodiment of the present disclosure, the second end 14 of the first flow path, the second end 24 of the second flow path and the second end 34 of the third flow path are connected. In some embodiments, the second end 14 of the first flow path, the second end 24 of the second flow path and the second end 34 of the third flow path may be directly connected. In the illustrated embodiment, the second end 14 of the first flow path is connected to a first pipeline 52 of an optional receiver 5, and the second end 24 of the second flow path and the second end 34 of the third flow path are connected to a second pipeline 53 of the receiver 5. The function of the receiver 5 is to store part of the refrigerant under a condition of excessive refrigerant, and to discharge the refrigerant when more refrigerant is needed.

The heat pump system further includes a switching assembly 90, which may be switched between any two, three or four of the following connection modes: a first connection mode, in which the first end 11 of the first flow path is connected to the outlet 41 of the compressor, and the first end 21 of the second flow path is connected to the inlet 42 of the compressor; a second connection mode, in which the first end 21 of the second flow path is connected to the outlet 41 of the compressor, and the first end 11 of the first flow path is connected to the inlet 42 of the compressor; a third connection mode, in which the first end 31 of the third flow path is connected to the outlet 41 of the compressor, and the first end 11 of the first flow path is connected to the inlet 42 of the compressor; and a fourth connection mode, in which the first end 31 of the third flow path is connected to the outlet 41 of the compressor, and the first end 21 of the second flow path is connected to the inlet 42 of the compressor. It should be understood that although the switching assembly 90 capable of being switched among four connection modes is described in the following embodiments, in some embodiments, the switching assembly 90 may only implement any two or three of the above connection modes. In some embodiments, the switching assembly 90 may be composed of a first four-way valve 91, a second four-way valve 92 and several pipelines. The specific operation will be described in detail below in conjunction with the operation modes.

The heat pump system also includes a control system, which controls the switching assembly 90, the first throttling device 13, the second throttling device 23 and optional components such as other valves and throttling devices in the heat pump system to achieve various functions, including operating the heat pump system in two, three or four of the cooling mode, the heating mode, the hot water preparing mode and the cooling heat recovery mode. Similarly, although the heat pump system having four modes is described below, the heat pump system may only have any two or three of the above modes in other embodiments.

As shown in FIG. 1, the heat pump system is in the cooling mode, and the switching assembly 90 is in the first connection mode, that is, the first four-way valve 91 is in a first position and the second four-way valve 92 is in a first position. At this point, the first throttling device 13 plays a throttling function, and the second throttling device 23 is fully opened. Specifically, in this cooling mode (cooling cycle), the refrigerant leaving the outlet 41 of the compressor enters the first four-way valve 91 from port a and leaves the first four-way valve 91 from port d, and enters the second four-way valve 92 from port e and leaves the second four-way valve 92 from port f thus passing through the first flow path 100 in the first flow direction. Specifically, the refrigerant passes through the first heat exchanger 12 and the first throttling device 13. The first throttling device 13 may be, for example, a thermal expansion valve or an electronic expansion valve, which plays a throttling function, that is, controlling the superheat degree of the refrigerant. After passing through the receiver 5, the refrigerant flows through the second flow path in the second flow direction, including the second throttling device 23 in a fully open state and the second heat exchanger 22. Finally, the refrigerant enters the second four-way valve 92 through port h and leaves the second four-way valve 92 from port g, passes through the separator 6, enters the inlet of the compressor 42 and is compressed by the compressor 4. It should be noted that in the embodiments of the present disclosure, in the cooling mode, the receiver 5 is always located downstream of the device 13 playing a throttling function, that is, it is in a low-pressure area. Therefore, the refrigerant that can be stored by the receiver 5 is in a low-pressure state, and a degradation of system performance caused by the storage of high-pressure refrigerant in the receiver 5 is avoided.

Next, reference is made to FIG. 2, in which the heat pump system is in the heating mode, and the switching assembly 90 is in the second connection mode, that is, the first four-way valve 91 is in the first position and the second four-way valve 92 is in a second position. At this point, the first throttling device 13 plays a throttling function, and the second throttling device 23 is bypassed. Specifically, the second throttling device 23 is bypassed by a second check valve 26 connected in parallel therewith. Specifically, in this heating mode (heating cycle), the refrigerant leaving the outlet 41 of the compressor enters the first four-way valve 91 from port a and leaves the first four-way valve 91 from port d, and enters the second four-way valve 92 through port e and leaves the second four-way valve 92 from port h, thus passing through the second flow path 200 in the first flow direction. Specifically, the refrigerant passes through the second heat exchanger 22 and bypasses the second throttling device 23; that is, through the second check valve 26 connected in parallel with the second throttling device 23, the second throttling device 23 (the second throttling device 23 itself is in a closed state) is bypassed, and the second check valve 26 only allows the fluid flowing toward the second end 24 of the second flow path to pass through. Then, after passing through the receiver 5, the refrigerant flows through the first flow path 100 in the second flow direction, including the first throttling device 13, which again plays a throttling function. The refrigerant then passes through the first heat exchanger 12, finally enters the second four-way valve 92 through port f and leaves the second four-way valve 92 from port g, passes through the separator 6, enters the inlet 42 of the compressor and is compressed by the compressor 4. In this embodiment, the second throttling device 23 can be bypassed by the second check valve 26 connected in parallel with the second throttling device 23, and the second check valve 26 has a lower flow resistance to high-pressure fluid.

Next, reference is made to FIG. 3, in which the heat pump system is in the hot water preparing mode, and the switching assembly 90 is in the third connection mode, that is, the first four-way valve 91 is in a second position and the second four-way valve 92 is in the second position. At this point, the first throttling device 13 plays a throttling function, and the second throttling device 23 is in a closed state. Specifically, in this hot water preparing mode (hot water preparing cycle), the refrigerant leaving the outlet 41 of the compressor enters the first four-way valve 91 from port a and leaves the first four-way valve 91 from port b, thus passing through the third flow path 300 in the first flow direction. Specifically, the refrigerant passes through the third heat exchanger 32 and the second check valve 33; then after passing through the receiver 5, the refrigerant flows through the first flow path 100 in the second flow direction, including the first throttling device 13, which again plays a throttling function. The refrigerant then passes through the first heat exchanger 12, finally enters the second four-way valve 92 through port f and leaves the second four-way valve 92 from port g, then passes through the separator 6, enters the inlet 42 of the compressor and is compressed by the compressor 4. In the hot water preparing mode, the third heat exchanger 32 supplies heat to water, thereby producing hot water.

Next, reference is made to FIG. 4, in which the heat pump system is in the cooling heat recovery mode, and the switching assembly 90 is in the fourth connection mode, wherein the first four-way valve 91 is in the second position and the second four-way valve 92 is in the first position. In this mode, the second throttling device 23 plays a throttling function, and the first throttling device 13 is in a closed state. Specifically, in this cooling heat recovery mode (cooling heat recovery cycle), the refrigerant leaving the outlet 41 of the compressor enters the first four-way valve 91 from port a and leaves the first four-way valve 91 from port b, thus passing through the third flow path 300 in the first flow direction. Specifically, the refrigerant passes through the third heat exchanger 32 and passes through the first check valve 33. Then, the refrigerant flows through the second flow path 200 in the second flow direction (without passing through the receiver 5), including the second throttling device 23 (the second check valve 26 does not allow the fluid in the second flow direction to pass through). In this cycle, the second throttling device 23 plays a throttling function, that is, the second throttling device 23 may be a thermal expansion valve or an electronic expansion valve, which plays a role of controlling the superheat degree. The refrigerant then passes through the second heat exchanger 22, finally enters the second four-way valve 92 through port h and leaves the second four-way valve 92 from port g, then passes through the separator 6, enters the inlet 42 of the compressor and is compressed by the compressor 4. In the cooling heat recovery mode, the second heat exchanger 22 performs cooling, and the third heat exchanger 32 recovers heat energy and supplies it to water, thereby producing hot water.

Therefore, in the embodiments according to the present disclosure, it is possible to use only two throttling devices to realize a free switching among the above four modes.

Next, reference is made to FIG. 5, which differs from the embodiments of FIGS. 1 to 4 in that the receiver 5 only has one pipeline 51, which is a common pipeline for liquid inflow and liquid outflow. In such an embodiment, the second end 14 of the first flow path, the second end 24 of the second flow path, and the second end 34 of the third flow path are directly connected, and the pipeline 51 of the receiver 5 may be connected to the first flow path, the second flow path or the third flow path at or near the point where the second end 14 of the first flow path, the second end 24 of the second flow path, and the second end 34 of the third flow path are connected. For example, the pipeline 51 of the receiver 5 may be connected to the first flow path at a position between the first throttling device 13 and the second end 14 of the first flow path, or connected to the second flow path on a main path between the second throttling device 23 and the second end 24 of the second flow path, or connected to the third flow path between the first check valve 33 and the second end 34 of the third flow path. The heat pump system according to the embodiment shown in FIG. 5 can also be operated in various modes, which will not be described repeatedly herein.

Next, referring to FIGS. 6-9, another embodiment according to the present disclosure will be introduced. This embodiment differs from the embodiments of FIGS. 1 to 4 in that the second end 14 of the first flow path and the second end 24 of the second flow path are connected to the first pipeline 52 of the receiver 5, and the second end 34 of the three-flow path is connected to the second pipeline 53 of the receiver 5. In addition, a solenoid valve 27 and a second check valve 26 are provided, which are connected between the second pipeline 53 of the receiver 5 (or the second end 34 of the third flow path) and a position between the second heat exchanger 22 and the second throttling device 23 on the second flow path. The solenoid valve 27 and the second check valve 26 are connected in parallel, and the second check valve 26 only allows the fluid flowing toward the second pipeline 53 of the receiver 5 (i.e., in the second flow direction) to pass through.

In this embodiment, in the cooling mode shown in FIG. 6, the refrigerant leaving the outlet 41 of the compressor passes through the switching assembly 90 and passes through the first flow path 100 in the first flow direction. At this point, the first throttling device 13 also plays a throttling function, the second throttling device 23 is closed, and the solenoid valve 27 is in an open state. After the refrigerant passes through the receiver 5, it bypasses the second throttling device 23 through the solenoid valve 27, enters the second heat exchanger 22, and returns to the inlet 42 of the compressor through the switching assembly 90.

In the heating mode shown in FIG. 7, the refrigerant leaving the outlet 41 of the compressor enters the second flow path 200 in the first flow direction through the switching assembly 90, the second throttling device 23 is closed, and the solenoid valve 27 is in a closed state. At this point, the high-pressure refrigerant passes through the second check valve 26 with a smaller pressure drop, passes through the receiver 5, and then flows through the first flow path 100 in the second flow direction. The first throttling device 13 plays a throttling function, and the refrigerant returns to the inlet 42 of the compressor through the switching assembly 90.

In the hot water preparing mode shown in FIG. 8, the refrigerant leaving the outlet 41 of the compressor passes through the switching assembly 90 and enters the third flow path 300 in the first flow direction, the second throttling device 23 is closed, and the solenoid valve 27 is in a closed state. At this point, the refrigerant flows through the first flow path 100 in the second flow direction after passing through the receiver 5, wherein the first throttling device 13 plays a throttling function, and the refrigerant returns to the inlet 42 of the compressor through the switching assembly 90.

In the cooling heat recovery mode shown in FIG. 9, the refrigerant leaving the outlet 41 of the compressor passes through the switching assembly 90 and enters the third flow path 300 in the first flow direction, the first throttling device 13 is closed, and the solenoid valve 27 is in the closed state. At this point, the refrigerant flows through the second flow path 200 in the second flow direction after passing through the receiver 5, wherein the second throttling device 23 plays a throttling function, and the refrigerant returns to the inlet 42 of the compressor through the switching assembly 90.

With the arrangement of FIGS. 6-9, the use of the solenoid valve to bypass the second throttling device 23 can achieve better performance in the cooling mode. It should be understood that in the embodiments of FIGS. 1 to 5, a solenoid valve connected in parallel with the second throttling device 23 may also be used to bypass the second throttling device 23 in the cooling mode to improve system performance. In addition, through the arrangements of FIGS. 6-9, the dual-pipeline receiver can also function in the cooling heat recovery mode, that is, the dual-pipeline receiver 5 can achieve the function of the adjusting the amount of refrigerant in the system in each of the four modes.

Next, reference is made to FIG. 10, which differs from the embodiments of FIGS. 6 to 9 in that the compressor 4 is an enhanced vapor injection compressor, which further includes an enhanced vapor injection port 43. The heat pump system also includes an economizer 8, and the first flow path 100 includes a branch point P, and a first pipeline 81 passing through the economizer 8, wherein in the heating mode and the hot water preparing mode, the refrigerant flowing from the second end 14 of the first flow path to the first end 11 of the first flow path passes through the first pipeline 81 of the economizer before passing through the first throttling device 13, and is divided at the branch point P into a first part leading to the first throttling device 13 and a second part leading to a branch. The second part of the refrigerant passes through an optional filter 85 and a branch throttling device 84 on the branch and a second pipeline 82 of the economizer 8 to exchange heat with the refrigerant in the first pipeline 81 of the economizer 8, and the refrigerant passing through the second pipeline 82 of the economizer 8 is supplied to the enhanced vapor injection port 43 of the compressor. The performance of the system can be further improved through the combination of the economizer and the enhanced vapor injection compressor. It should be understood that the combination of the economizer and the enhanced vapor injection compressor in FIG. 10 may also be applied to other embodiments of the present disclosure.

In the embodiments of the present disclosure, only two sets of throttling devices are required to be used to switch between the four modes, which saves the cost of more throttling devices or control valves. In some embodiments, the third flow path does not include a throttling device, and only the first throttling device 13 and the second throttling device 23 are present on the three flow paths. In addition, in the embodiments according to the present disclosure, in the cooling mode, the receiver is located in a low-pressure area downstream of the throttling device, thereby improving the performance of the heat pump system in the cooling mode.

The heat pump system includes a cooling working condition, and under the cooling working condition, the heat pump system is switched among the cooling mode, the hot water preparing mode, and the cooling heat recovery mode. For example, when there is a demand for cooling, the heat pump system is switched to the cooling mode; when there is a demand for hot water preparation, the heat pump system is switched to the hot water preparing mode; and when there are demands for both cooling and hot water preparation, the cooling heat recovery mode is executed.

The heat pump system also includes a heating working condition, and under the heating working condition, the heat pump system is switched between the heating mode and the hot water preparing mode. For example, when there is a demand for heating, the heat pump system is switched to the heating mode; and when there is a demand for hot water preparation, the heat pump system is switched to the hot water preparing mode. In addition, under the heating working condition, the heat pump system can defrost the first heat exchanger 12 by being switched to the first connection mode and fully opening the first throttling device.

In another aspect, a control method of a heat pump system is also provided, which includes: operating the heat pump system in any two, three, or four of a cooling mode, a heating mode, a hot water preparing mode, and a cooling heat recovery mode; wherein:

in the cooling mode, the first end of the first flow path is connected to the outlet of the compressor, the first end of the second flow path is connected to the inlet of the compressor, the first throttling device plays a throttling function, and the second throttling device is fully opened or bypassed;

in the heating mode, the first end of the second flow path is connected to the outlet of the compressor, the first end of the first flow path is connected to the inlet of the compressor, the first throttling device plays a throttling function, and the second throttling device is bypassed;

in the hot water preparing mode, the first end of the third flow path is connected to the outlet of the compressor, the first end of the first flow path is connected to the inlet of the compressor, the first throttling device plays a throttling function, and the second throttling device is closed; and

in the cooling heat recovery mode, the first end of the third flow path is connected to the outlet of the compressor, the first end of the first flow path is connected to the inlet of the compressor, the second throttling device plays a throttling function, and the first throttling device is closed.

The specific embodiments described above are merely for describing the principle of the present disclosure more clearly, and various components are clearly illustrated or depicted to make it easier to understand the principle of the present disclosure. Those skilled in the art can readily make various modifications or changes to the present disclosure without departing from the scope of the present disclosure. Therefore, it should be understood that these modifications or changes should be included within the scope of protection of the present disclosure. 

What is claimed is:
 1. A heat pump system, comprising: a compressor; a first flow path, which comprises a first end of the first flow path, a first heat exchanger, a first throttling device, and a second end of the first flow path in sequence; a second flow path, which comprises a first end of a second flow path, a second heat exchanger, a second throttling device, and a second end of the second flow path in sequence; a third flow path, which comprises a first end of the third flow path, a third heat exchanger, a first check valve, and a second end of the third flow path in sequence, wherein the first check valve on the third flow path only allows a fluid flowing in a direction toward the second end of the third flow path to pass through; wherein the second end of the first flow path, the second end of the second flow path and the second end of the third flow path are connected; a switching assembly, which can be switched between any two, three or four of the following connection modes: a first connection mode, in which the first end of the first flow path is connected to an outlet of the compressor, and the first end of the second flow path is connected to an inlet of the compressor; a second connection mode, in which the first end of the second flow path is connected to the outlet of the compressor, and the first end of the first flow path is connected to the inlet of the compressor; a third connection mode, in which the first end of the third flow path is connected to the outlet of the compressor, and the first end of the first flow path is connected to the inlet of the compressor; and a fourth connection mode, in which the first end of the third flow path is connected to the outlet of the compressor, and the first end of the second flow path is connected to the inlet of the compressor; and a control system, which enables the heat pump system to operate in any two, three, or four of a cooling mode, a heating mode, a hot water preparing mode, and a cooling heat recovery mode; in the cooling mode, the switching assembly is switched to the first connection mode, the first throttling device plays a throttling function, and the second throttling device is fully opened or bypassed; in the heating mode, the switching assembly is switched to the second connection mode, the first throttling device plays a throttling function, and the second throttling device is bypassed; in the hot water preparing mode, the switching assembly is switched to the third connection mode, the first throttling device plays a throttling function, and the second throttling device is in a closed state; and in the cooling heat recovery mode, the switching assembly is switched to the fourth connection mode, the second throttling device plays a throttling function, and the first throttling device is in a closed state.
 2. The heat pump system according to claim 1, wherein the second flow path comprises a second check valve connected in parallel with the second throttling device, and the second check valve only allows a fluid flowing in a direction toward the second end of the second flow path to pass through.
 3. The heat pump system according to claim 1, wherein the second flow path comprises a solenoid valve connected in parallel with the second throttling device, and in the cooling mode, in the heat pump system, the solenoid valve is opened and the second throttling device is closed to bypass the second throttling device.
 4. The heat pump system according to claim 1, wherein the heat pump system further comprises a receiver, and the receiver comprises a single pipeline and is connected to or near a position where the second end of the first flow path, the second end of the second flow path and the second end of the third flow path are connected.
 5. The heat pump system according to claim 1, wherein the heat pump system further comprises a receiver which comprises a first pipeline and a second pipeline, the second end of the first flow path and the second end of the second flow path are connected to the first pipeline of the receiver, and the second end of the third flow path is connected to the second pipeline of the receiver.
 6. The heat pump system according to claim 5, wherein the heat pump system further comprises a solenoid valve, which is connected between the second pipeline of the receiver and a position on the second flow path between the second heat exchanger and the second throttling device.
 7. The heat pump system according to claim 5, wherein the heat pump system further comprises a second check valve, which is connected between the second pipeline of the receiver and a position on the second flow path between the second heat exchanger and the second throttling device, and which only allows a fluid flowing in a direction toward a second end of the second pipeline to pass through.
 8. The heat pump system according to claim 1, wherein the heat pump system comprises a cooling working condition, and under the cooling working condition, the heat pump system is switched among the cooling mode, the hot water preparing mode, and the cooling heat recovery mode; and/or the heat pump system comprises a heating working condition, and under the heating working condition, the heat pump system is switched between the heating mode and the hot water preparing mode, wherein the heat pump system performs defrosting by being switched to the first connection mode and fully opening the first throttling device.
 9. The heat pump system according to claim 1, wherein the compressor is an enhanced vapor injection compressor, the heat pump system further comprises an economizer, and the first flow path comprises a branch point and passes through a first pipeline of the economizer, and wherein in the heating mode and the hot water preparing mode, a refrigerant flowing from the second end of the first flow path toward the first end of the first flow path passes through the first pipeline of the economizer before passing through the first throttling device, and is divided at the branch point into a first part leading to the first throttling device and a second part leading to a branch; the second part of the refrigerant passes through a branch throttling device on the branch and a second pipeline of the economizer to exchange heat with the refrigerant in the first pipeline of the economizer, and the refrigerant passing through the second pipeline of the economizer is supplied to an enhanced vapor injection port of the compressor.
 10. The heat pump system according to claim 1, wherein the third flow path does not have a throttling device.
 11. The heat pump system according to claim 1, wherein the switching assembly comprises two four-way valves.
 12. A control method of a heat pump system, the heat pump system comprising: a compressor; a first flow path, which comprises a first end of the first flow path, a first heat exchanger, a first throttling device, and a second end of the first flow path in sequence; a second flow path, which comprises a first end of a second flow path, a second heat exchanger, a second throttling device, and a second end of the second flow path in sequence; a third flow path, which comprises a first end of the third flow path, a third heat exchanger, a first check valve, and a second end of the third flow path in sequence, wherein the first check valve on the third flow path only allows a fluid flowing in a direction toward the second end of the third flow path to pass through; wherein the second end of the first flow path, the second end of the second flow path and the second end of the third flow path are connected; wherein the method comprising: operating the heat pump system in any two, three, or four of a cooling mode, a heating mode, a hot water preparing mode, and a cooling heat recovery mode; wherein: in the cooling mode, the first end of the first flow path is connected to the outlet of the compressor, the first end of the second flow path is connected to the inlet of the compressor, the first throttling device plays a throttling function, and the second throttling device is fully opened or bypassed; in the heating mode, the first end of the second flow path is connected to the outlet of the compressor, the first end of the first flow path is connected to the inlet of the compressor, the first throttling device plays a throttling function, and the second throttling device is bypassed; in the hot water preparing mode, the first end of the third flow path is connected to the outlet of the compressor, the first end of the first flow path is connected to the inlet of the compressor, the first throttling device plays a throttling function, and the second throttling device is closed; and in the cooling heat recovery mode, the first end of the third flow path is connected to the outlet of the compressor, the first end of the first flow path is connected to the inlet of the compressor, the second throttling device plays a throttling function, and the first throttling device is closed.
 13. The method according to claim 12, wherein the method comprises: operating the heat pump system under a cooling working condition, wherein the heat pump system is switched among the cooling mode, the hot water preparing mode, and the cooling heat recovery mode; and/or operating the heat pump system under a heating working condition, wherein the heat pump system is switched between the heating mode and the hot water preparing mode; the method further comprises: under the heating working condition, connecting the first end of the first flow path to the outlet of the compressor, connecting the first end of the second flow path to the inlet of the compressor, and fully opening the first throttling device to perform defrost. 